nob_reframe360 (Compatible with IFFS 2025.1.0 and up)
This Matchbox shader reframes spherical footage in equirectangular format to rectilinear images.
Image-wise only spatial transformations are applied to acquire the planar view, thus brightness is retained.
The resulting image format can be customized to any canvas resolution as well as frame and pixel aspect ratios, downscaling being a particular strength of this shader and its filtering options.
By default, antialiasing is disabled for performance reasons, though it is strongly encouraged to enable it for final output. Filtering is done through either a Box- or a Gauss-Kernel, the former - in combination with a width of 1, corresponding to the default
Optionally, lens-distortion can be added to the output, either through numeric parameters or an external ST map. The latter is implicitly expected to be of equal format to the output, fully compatible with
For enhanced performance, this shader internally uses a ST map representing the aggregate transformation which itself is bilinearly filtered; the nature of which is well behaved for typical use, resulting in negligible interpolation errors. Supersampling then takes place on the application of this ST map.
Note that this may cause a loss of information for border pixels, which would interpolate from sample locations outside the target-frame.
To eliminate this error, one can specify a higher & wider canvas resolution, accommodating the filtering kernel size; to then crop the output to the desired format using the <Resize & Crop> node.
Make sure to maintain correct pixel- & frame aspect ratios between reframing & crop. Use the
Upressing is best done with other means than this shader, since significant enlargements on pixel-level might result in strong pixelation. This is especially true for 360° footage, and unless reframing a source at least 8 times the resolution of the output format (64 times the pixel number) with not too narrow a field of view - smoother external filtering such as linear or EWA+linear might be preferable.
For this, one can output the intermediate ST map.
The ST map generated doesn’t wrap in S-dimension, thus repeating wrapping to normalized values might be required. Additionally, since mapping equirectangular to rectilinear coordinates inevitably results in lines of discontinuity for S; a second map for S - with the discontinuity shifted by 180 degrees - is calculated and stored to the blue channel. The matte output for STs is white where the blue channel holds continuous data for S, and black for the green one.
Adaptive Degradation is supported by this shader, which if active bypasses antialiasing.
This shader is licensed under the terms of the MIT license.
For questions contact:
nobbl211 _at_ gmail.com
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